The invention relates to a method for changing the lift of inlet valves of an internal combustion engine between a partial lift and a full lift under the control of at least one camshaft having partial lift cams and full lift cams.
Such a method is known from MTZ 61 (2002), pages 730-746. In this method, changeover is effected between an inner tappet and an outer tappet, which are assigned to different cam profiles and act on the inlet valve, by means of a controllable cup tappet. The inner tappet or partial lift cam is designed in such a way that it generates a lift of the inlet valve of roughly 3 mm, whereas the outer tappet or full lift cam generates an inlet valve lift of roughly 12 mm.
For low power requirements of the internal combustion engine, the small inlet valve lift is activated, whereby consumption and emissions are lowered. As soon as the driver of a vehicle in which the internal combustion engine is installed requests a higher torque, changeover takes place to that tappet or cam which generates the larger inlet valve lift.
In this connection, however, it is problematic that, when changing over between the partial lift and the full lift of the inlet valves, a relatively great torque jump occurs because of the much greater cylinder filling via the increased inlet valve flow cross-section which the driver may experience as unpleasant.
In the prior art referred to above, this torque jump is compensated in a relatively complicated way by adaptation of the mixture within the cylinder, by changing the throttle valve angle and by adjusting the ignition angle. Changing the throttle valve angle in particular, and consequently the adaptation of the fresh air mass flow into the internal combustion engine, is a very problematic and complex operation, however, which moreover cannot be carried out within a single load change cycle of the internal combustion engine.
U.S. Pat. No. 5,009,203 describes a method for controlling the valve changeover in an internal combustion engine in which the changeover is to be carried out in such a way that the internal combustion engine delivers essentially the same torque before and after changeover. In order to achieve this, the fuel quantity injected is measured before and after changing over.
The method described therein does not allow independent adjustment of the inlet valve control timing and of the inlet valve lift, however, so that changeover is relatively rigid.
Based on the prior art described in MTZ 61 (2002), it is the object of the present invention to provide a method for changing the lift of inlet valves of an internal combustion engine so that a changeover between a partial lift and a full lift of the inlet valves can be carried out within a very short time and with a great variability with regard to the control time and the valve lift.